1. Field of the Invention
This invention relates to a resistance change memory device, specifically to high-speed write mode thereof in a case where the memory device is integrated with a large capacity.
2. Description of the Related Art
A resistance change memory (i.e., resistive RAM; ReRAM), in which the resistance state of cells is exchanged by voltage, current or heat and it serves as data, is noticed for succeeding a conventional NAND type flash memory. The ReRAM is suitable for shrinking the cell size and for constituting a cross-point cell array, and the cell arrays may be easily stacked. Therefore, it is noticed that a large capacity of file memory may be constructed as a three-dimensional (3D-) cell array. For example, refer to Y. Hosoi et al, “High Speed Unipolar Switching Resistance RAM(RRAM) Technology” IEEE International Electron Devices Meeting 2006 Technical Digest p. 793-796.
What is material to achieve a large capacity of ReRAM and a high-speed read/write property is that there are asymmetric characteristics between the reset and set operations of a ReRAM. In detail, there is such a basic difference in case of a kind of memory cell material that the set operation is a voltage mode while the reset operation is a current mode. Another asymmetric property is in that the reset operation of the current mode needs a long time such as several times to one hundred times in comparison with the set operation of the voltage mode. Note here that if the cell material is changed, the above-described time relationship between the reset and set operations may be reversed.
Which of the voltage mode and current mode takes a long time is dependent on the cell material. If not considering sufficiently the above-described asymmetric properties of the reset and set operations, it becomes difficult to achieve a high performance ReRAM with a large capacity.